The present invention is in the field of battery technology, and more particularly in the area of using additives to enhance electrolyte and electrode performance in metal-fluoride and carbon-fluoride batteries.
One type of battery consists of a negative electrode made primarily from lithium and a positive electrode made primarily from a compound containing carbon and fluorine. These batteries can be referred to as lithium/carbon-fluoride batteries or Li—CF batteries.
Lithium/carbon-fluoride batteries are used extensively in medical application, as back-up power electronics, military applications, and in other settings. Lithium/carbon-fluoride batteries have the highest specific energy of any batteries currently commercially available.
During discharge, lithium ions and electrons are generated from oxidation of the negative electrode while fluoride ions and carbon or produced from reduction of the positive electrode. The generated fluoride ions react with lithium ions near the positive electrode to produce a compound containing lithium and fluorine, which may deposit at the positive electrode surface.
Lithium/carbon-fluoride batteries enjoyed widespread use in commercial applications in part due to certain desirable characteristics. The carbon-fluoride positive electrode is lightweight, which makes the battery desirable in portable or mobile applications where weight is an important design consideration. Also, the carbon-fluoride positive electrode has a high capacity. Further, the overall reaction has a high electrochemical potential.
Despite their widespread use, lithium/carbon-fluoride batteries suffer from certain challenges.
The carbon-fluoride compound and the lithium-fluoride compound have comparatively low electrical conductivity as compared to certain other battery materials. Such comparatively low electrical conductivity can have the following results in electrochemical cell: comparatively low power; comparatively low operating voltage; comparatively large underpotential upon discharge; and the comparatively low capacity during a high rate of discharge.
The carbon-fluoride compound and the lithium-fluoride compound have comparatively low thermal conductivity as compared to certain other battery materials and such comparatively low thermal conductivity can result in comparatively significant heat generation by the electrochemical cell upon discharge.
Breaking the carbon-fluoride bonds of the carbon-fluoride compound requires a comparatively high activation energy as compared to certain other battery materials. Such comparatively high activation energy for bond breaking can have the following results and electrochemical cell: comparatively low power; comparatively low operating voltage; comparatively large under potential upon discharge; comparatively low capacity during a high rate of discharge; and comparatively significant heat generation upon discharge.
Metal-fluoride batteries have many of the same problems. Additionally, rechargeable metal-fluoride batteries have a large overpotential during charging, resulting in a poor energy efficiency.
There have been prior attempts to address such challenges. One prior attempt involves forming a composite positive electrode. The raw composite material contains a carbon-fluoride compound and a second compound, which is comparatively more electrically conductive than the carbon-fluoride compound. These two compounds are mixed together to form a composite material that is then formed into a positive electrode.
One example of such composite material is a carbon-fluoride compound composited with silver vanadium oxide (silver vanadium oxide is often abbreviated as “SVO” in the battery industry rather than by its periodic table symbols). This CFx/SVO composite material has been used to form a positive electrode and a battery for use in medical devices and has demonstrated increased pulse power and increased energy density when compared to a battery using a positive electrode formed only from carbon-fluoride.
CFx/SVO composite or hybrid cathode materials can exhibit high energy and high pulse power. However, in batteries using CFx/SVO hybrid cathode materials, power can degrade below critical limits for particular devices at a late depth of discharge.
Another example of a composite material for use in forming a positive electrode is a carbon-fluoride compound composited with manganese dioxide (MnO2). This CF/MnO2 composite material has been used to form a positive electrode where cost is a key design factor and has demonstrated increased power at high discharge rates, increased energy density, and reduced heat buildup in the electrochemical cell when compared to a battery using a positive electrode formed only from carbon-fluoride.
Although prior batteries using positive electrodes formed from these and certain other composite materials generally have higher power, higher operating potential, lower under potential, and less heat build up when compared to batteries using a positive electrode formed only from metal-fluoride or carbon-fluoride, the performance of electrochemical cell could be improved significantly. Also, certain of these performance improvements come at the expense of reduced energy density.
Certain embodiments of the present invention address the challenges found in batteries. Certain embodiments of the present invention can be used to form electrochemical cells for batteries that exhibit lower under potential, higher power, higher capacity at a high discharge rate, less heat generation, or faster heat dissipation when compared to prior batteries.
These and other challenges can be addressed by embodiments of the present invention described below.